XPost: rec.radio.amateur.policy, uk.radio.amateur   
   From: wilson@math.wisc.edu   
      
   On 3/3/2021 2:34 PM, Ian Jackson wrote:   
   > In message , Jimmy Stewart ...   
   >  writes   
   >> On 03/03/2021 16:11, Brian Morrison wrote:   
   >>> On Wed, 03 Mar 2021 14:45:20 +0000, Jimmy Stewart ... wrote:   
   >>>   
   >>>>> The problem was that in a supermarket carpark, customers were having   
   >>>>> trouble locking and unlocking their cars. Is it possible that the   
   >>>>> OFCOM   
   >>>>> engineer actually found that he needed to do a bit of urgent   
   >>>>> on-the-job   
   >>>>> shopping?   
   >>>> I used to stop lazy buggers getting into their cars parked in the drop   
   >>>> off zone at a local car park by calling cq on 70cm ...   
   >>>  As you are a licensed user of the frequency, you have priority over the   
   >>> unlicensed, unprotected short range devices used for these purposes. Of   
   >>> course people who are not aware of this still get annoyed when their key   
   >>> fobs don't get received by the nasty super-regen receivers in their car.   
   >>> They should direct their annoyance at the PTTs who decided the 433MHz   
   >>> ISM   
   >>> allocation should go ahead in the mid 1980s.   
   >>>   
   >> bitter bitter and twisted....best use for the 70Cm band   
   >   
   > With my last two cars, the range that I can lock and unlock is at least   
   > 100 yards. Is this not far too great? Either the receiver is far too   
   > sensitive, or the fob TX too powerful. I would have thought that a range   
   > of a few feet would be sufficient, and reduce the likelihood of the   
   > receiver getting blocked. There's also the question of criminals nearby   
   > intercepting your fob signal, recording it and using it to open your car   
   > the moment your back is turned.   
      
   A contemporary lock system of this sort should not be vulnerable to   
   playing back a recording. The key structure "rotates" from one use to   
   the next, so the right thing to send last time is not the same as now.   
      
   That "record and playback" vulnerability was taken away years ago. That   
   is why you have to synchronize the fob with the system if you get a new   
   one, or (on older ones that had them) if you replace a battery.   
      
   But I am not arguing that the transmitter could not be too powerful,   
   just for other reasons.   
      
   Bob W, WA9D   
   (from the other side of the pond... I don't know if our FCC will be   
   following OFCOM.)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)